Tuesday, May 23, 2017

A rotameter is one particular type of variable area flowmeter that measures flow by varying the cross-
sectional area a fluid or gas travels through in a closed tube.

Advantages

Requires no external power.

Is a simple device that can be easily manufactured out of inexpensive materials.

Linear scale.

The clear glass tube is resistant to thermal shock and chemical reaction.

Disadvantages

Must be mounted vertically, with designated top and bottom, and with the fluid flowing from bottom to top.

Graduations on a given rotameter are only accurate for a given substance at a given temperature. Separate rotameters must be used for fluids with different densities and viscosities, or multiple scales on the same rotameter must be used.

Resolution is relatively poor and gets worse near the bottom of the scale.

Custom heating element design is best completed and accomplished through the proper application of the right resources. The local heating element sales engineer is an access point to high level technical knowledge and assistance that can be easily tapped and brought to bear on your successful task or project completion.

Product Knowledge: The heating element sales rep will be current on product offerings, proper application, and capabilities. They also have information regarding what products may be obsolete in the near future. This is an information source at a level not generally accessible to the public via the Internet.

Application Experience: As a project engineer, you may be treading on fresh ground regarding some aspects of your current assignment. There can be real benefit in connecting to a source who has decades of designing electrical heating elements.

Access: Through a heating element sales rep, you may be able to establish a connection to “behind the scenes” manufacturer contacts who will champion your project internally. The rep knows people, makes it his/her business to know the people that can provide answers, and can act as your projects ambassador with the manufacturer.

Certainly, any solutions proposed are likely to be based upon the products sold by the representative. That is where considering and evaluating the benefits of any proposed solutions become part of achieving the best project outcome.

Develop a professional, mutually beneficial relationship with a heating element sales rep. Their success is tied to your success and they are eager to help you.

Saturday, May 13, 2017

Cartridge heaters provide localized heat to restricted work areas requiring close thermal control. Dies, platens and a variety of other types of processing equipment are efficiently heated. Closely controlled work temperatures up to 1400° F (760° C) are obtained by a combination of heater location and proper wattage output.

Heater Life

Cartridge heater life is determined by how efficiently the heat generated in the resistance wire can be conducted away from the wire and into the part being heated. The efficiency of heat transfer is generally controlled by three factors:

Resistance wire watt density

Density of insulating material around the wire

Fit of the heater into the heated part

There are two basic designs of cartridge heaters - swaged and standard. Although both type heaters look identical, the internal construction is very different.

Standard Cartridge Heater Design

Standard Cartridge Heater Design

Nichrome wire heating coils are inserted in holes formed in ceramic tubes. Pure magnesium oxide filler is vibrated into the holes housing the heating coils to allow maximum heat transfer to the stainless steel sheath. The heater then has a Heliarc welded end cap inserted on the bottom of the heater and insulated leads are installed. The MGO powder is not compacted and heat transfer is a function of the grain-to-grain thermal conductivity to the heater sheath, and then into the heated part. Because of this, the heater wire watt densities must be kept in the low to medium range.

Swaged Cartridge Heater Design

Swaged Cartridge Heater Design

Swaged cartridge heaters wind Nichrome wire around a precision ceramic core and the carefully position the resistance wire and ceramic core uniformly inside the the heater sheath. Pure magnesium oxide (MgO) powder is then vibrated in and the heater is swaged to a specific diameter. Swaging is a process that mechanically forces the heater through a confining die to reduce its diameter and thus compact the powdered MgO to rock-like consistency for greater thermal conductivity. This compressed MGO transfers the heat from the resistance wire much more efficiently. The improved heat transfer allows for higher wire watt densities allowing swaged cartridge heaters to operate at higher temperatures.

Cartridge Heater Fit

The most common cause of cartridge heater failure is an improper fit in the hole into which it is inserted. If the heater is surrounded by air, an excellent thermal insulator, it cannot dissipate it's heat into the part with optimum efficiency. The result is much higher temperatures on the Nichrome wire and failure. The goal to longer life with cartridge heaters is to accommodate the tightest fit practical for a given application.

In summary, if you want the longest life cartridge heater, choose a swaged heater and make sure you provide a machined, close tolerance fit between the outside diameter of the heater and the inside diameter of the hole.

Monday, May 8, 2017

Vacuum and ultra-clean manufacturing applications have continuously challenged designers with the need for versatile and cost effective ways to get power, control signals, fiber optic, and pneumatic lines in and out of a vacuum.

Failures due to contamination, dust, or leaks can be devastatingly costly, in both money and time.

Historically, glass-to-metal (GTM) hermetic seals have been used, but their limited size, shape, pin options, and shielding limitations have frustrated designers. A more accommodating and cost effective feedthrough solution was badly needed.

Enter epoxy potted feedthroughs. While GTM has a distinct advantage in very high temperature applications, in low-to-medium temperature applications newer epoxy resins are quickly gaining ground. Ideally suited for use where continuous temperatures stay under 200 deg. C , the versatility and cost of epoxy feedthroughs make them a clearly better choice. Additionally, in many cases epoxy feedthroughs can be prototyped and small quantities can be provided much more quickly.

Ultimately, epoxy vacuum feedthrough’s greatest advantage is their design versatility and option flexibility. Flanges, threaded connections, circuit board mounts, 120 volt receptacles, thermocouples, pneumatic tubes, Sub D connectors, and fiber optic cables are all examples of options that are easily accommodated. No longer does a designer have to conform their design to a standard glass-to-metal specification. Epoxy vacuum feedthroughs give designers the freedom to have a feedthrough that exactly meets their needs.

Saturday, May 6, 2017

By understanding the most common reasons cartridge heaters fail, users can take preventative steps in their applications to achieve optimum heater life and lower equipment ownership costs.

Improper Fit
The most common cause of cartridge heater failure is an improper fit in the hole into which it is inserted. If the heater cannot dissipate the heat being generated and produced by contact with the sheath, the temperature inside the heater will continue to rise until the heater fails.

Moisture and/or Impurities
The MGO used in cartridge heaters is hydroscopic. Every time power to electric heaters is eliminated, an internal vacuum occurs which draws in air from the surrounding area. If moisture or impurities (oil, gas, etc.) are present, they can be drawn in to the heater, and cause a short circuit resulting in a heater failure.

Watt Density is Too High
If the watts/square inch is excessive, the heater will not be able to dissipate the heat and the heater will fail.

Incorrect Voltage Applied
The wattage of any electric heater varies as the square of the voltage. If a 120 Volt heater is powered on 240 Volts, the wattage will be 4 times greater than that for the same 120 Volt heater. Under normal conditions, this may result in heater failure.

Frequent Temperature Cycling
Rapid cycling of heaters from very low to very high temperatures shortens their life considerably.